Summary of Work: This project is designed to determine the relationships among DNA repair, chromosome structure, and mutagenesis in Drosophila melanogaster. Mutations that increase the mutant frequency (mutators) have been identified in the mu2 gene and characterized. These mutations appear to disrupt chromatin structure in the oocyte, but not the sperm chromosomes, so that oocyte chromosomes are not repaired properly, and instead are "capped" with a new telomere. Given that mu2 mutations also increase mitotic recombination, it is reasonable to expect that the MU2 protein also associates with somatic chromosomes. This is supported by the observation that mu2 mRNA is found in oocytes and some somatic tissues, but not testes. Two independent mutant alleles greatly reduce mu2 mRNA in these tissues. The mu2 gene sequence does not have a strong resemblance to any other genes in the database, although the carboxy half of the protein is extremely basic and lysine-rich, consistent with the notion that the protein associates with chromatin. The genomic region including the mu2 transcription unit has been reintroduced into the genome and shown to complement mu2 mutations. Antibodies have been made to the MU2 protein and will be used to ascertain intracellular localization. We also plan to look for other gene products that might interact with MU2 using the yeast two-hybrid system.